Heat and abrasion resistant textiles

ABSTRACT

A TEXTILE (SUCH AS A FIBER OR FABRIC) OF HIGH ABRASION AND HEAT RESISTANCE AND HIGH FOLD ENDURANCE IS PROVIDED BY A STRUCTURE COMPRISING A HIGH MELTING TEXTILE SUBSTRATE (SUCH AS GLASS) BEARING A COAING OF POLYTETRAFLUOROETHYLENE (PTFE) WHICH COATING CONTAINS FROM ABOUT 1% TO ABOUT 30% BY WEIGHT BASED ON THE SAID COABOUT 1% TO HAR , WATER INSOLUBLE PARTICULATE FILLER OF ONE TO 75 MICRONS DIAMETER.

United States Patent 3,709,721 HEAT AND ABRASION RESISTANT TEXTILESJames Ping King, Lansdale, Pa., assignor to Pennnwalt Corporation,Philadelphia, Pa. No Drawing. Filed Sept. 14, 1970, Ser. No. 72,226 Int.Cl. B44d 1/08, N02

US. Cl. 117-104 R 7 Claims ABSTRACT OF THE DISCLOSURE A textile (such asa fiber or fabric) of high abrasion and heat resistance and high foldendurance is provided by a structure comprising a high melting textilesubstrate (such as glass) bearing a coating of polytetrafiuoroethylene(PTFE) which coating contains from about 1% to about 30% by weight basedonthe said coating of a hard, water insoluble, particulate filler of oneto 75 microns diameter.

BACKGROUND OF THE INVENTION The use of polytetrafluoroethylene (PTFE)coatings upon textiles is well known in the art. It is known to be ofparticular value in coating textiles formed from fibrous materials of abrittle nature, particularly those of an inorganic nature such as glass,asbestos (U.S. 3,347,737) and graphite, (U.S. 3,108,018) to improvesurface lubricity. Coating compositions useful in im pregnatingsubstrates such as glass fibers or glass cloth are taught in US.2,562,117 (which teaches a liquid coating composition containing PTFEand chromic acid), US. 2,562,118 (which provides a liquid coatingcomposition containing PTFE, chromic acid and phosphoric acid), US.2,613,193 (showing a sprayable PT FE aqueous suspensoid containing PTFE,a wetting agent, Water and an organic liquid) and US. 2,710,266 (whichdescribes an aqueous dispersion of colloidal PTFE containing an alkalimetal silicate). Despite the improved strength and surface lubricityattributable to the PTFE coating, such coated structures still possess arelatively low abrasion resistance and fold endurance, limiting theirpractical usefulness. Some of these coated structures also tend to storeelectrical charges making them unsuitable for uses where staticelectricity is to be avoided.

SUMMARY OF THE INVENTION In accordance with the present invention, atextile is provided which bears a coating of PTFE, which coatingcontains from about 1% to about 30% by weight based on the said coatingof a hard particulate filler of from one to 75 microns in diameter. Theresulting textile is characterized by high abrasion resistance and highfold endurance. When the particulate matter is metallic, the structuresare also found to possess high electrical conductivity and ability todissipate static charge.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the examples which follow,abrasion resistance is measured by the ASTM-D-1044 method, using a TaborAbrasor Model 505 with a CS-17 head under a 500 gram load and for 1000cycles. Folding endurance is determined using the method described inASTM-D- 217-6 employing a 1000 gram load, the figure given being anaverage of five samples measured in each direction. Unless otherwiseindicated, static charge in coulombs is measured on a Sweeney FabricStatic Charge Tester Model No. SWE-1190 at C. and 50% relative humidityand surface resistivity, in ohms/cm. is measured at 25 C. and 10%relative humidity. In each example, grams of an aqueous emulsioncontaining about PTFE resin as the dispersed phase and having 1.5

gram of filler with a particle size of at least one micron suspended init, is sprayed on both sides of a piece of plain weave, siliconefinished glass fabric (7 mils). The silicone finish is not essential andwhen it is desired on the glass fabric, it is applied by spraying thefabric on each side with commercially available silane or siliconefinishes such as alpha-methacryloxypropyl-trimethoxysilane oralpha-aminopropyltriethoxysilane followed by drying and curing thesilicon finish under conditions prescribed by the manufacturer. Typicalsilicone finishes are sold by Union Carbide Corporation under thedesignation APl3l and AP134 by I. P. Stevens, Inc. as I. P. Stevens9362. The mechanical properties of the PTFE coated structure aresubstantially unaffected by changing the silicone finish. Afterapplication of the PTFE emulsion, the fabric is dried in air at roomtemperature and then cured at 380 C. for the indicated periods. Theobserved static charges and resistivities of the resulting fabrics arereported in the table.

TAB LE PTFE emulsion B Static charge (coulomb) Cure period Resistivity(min.)

0 1m 4. 1x12 2. 3X10" 1.4)(10 2. 6X10 Ex. Filler 1 Stainless steeL-852-202 2 Aluminum 850-202 3 gun. Stainless steel-.- 850-20l 6 AluminumNone The final thickness of the fabric of Example 1 is observed to be9.5 mils and has an abrasion resistance of 28:6 mg. and a foldingendurance of 93000il3000 cycles. Abrasion resistance of the fabric inExample 6 is about 46 mg.

The textile which forms the substrate can by any kind of fiber such asstaple, floc, yarn (either continuous or spun) or fabric (woven, knittedor of non-woven variety). It is essential, of course, that the substratetextile not melt or decompose at temperatures used for the curing ofPTFE. Generally, any material is suitable which will tolerate exposureto a temperature of about 400 C. The textile may be either inorganic ororganic. Among suitable inorganic materials are asbestos, glass, silica,silicon carbide, alumina and high melting metals. Among the organicmaterials are carbon, graphite, PTFE fibers, the high meltingpolyamides, polyurethanes and polyamides (such as the wholly aromaticpolyamides disclosed in US. 3,094,511 and 3,287,324 and the acid-graftedpolyamides disclosed in US. 3,099,631).

PTFE Application Technique The PTFE is preferably applied to the textilesubstrate from an emulsion using a spray, dip or padding technique. Apre-treatment of the textile substrate with a silicone compound asdescribed above may be included but is not essential. Preferably, thePTFE emulsion contains an adhesive such as the emulsion designated No.852- 202 available from E. I. du Pont de Nemours & Co. Generally suchemulsions (preparation of a typical type of which is described in US.2,613,193) contain a surfactant such as a long chain alkyl arylpolyether alcohol (e.g., octyl phenyl polyglycol ether) and contain fromabout 50 to 60% solids of which about by weight if PTFE. The use ofchromic acid and combinations of chromic acid and phosphoric acid aswell as alkali metal silicates to improve adhesion to the substrates isknown in the art as pointed out previously above.

3 Fillers Percent Largest size particle retained in screen:

74 microns (200 mesh) 100 44 microns (325 mesh) 98 20 microns 65 microns31 Larger sized filler particles tend to settle'to the bottom of theirmixtures with PTFE emulsions. However, the emulsion may be agitatedprior to use in order to resuspend the larger particles. The fillerparticle have a hardness on the Mohs scale of at least 1 and preferablyof 6.

Any filler compatible with PTFE can be used in the present invention.Compatibility with PTFE is used in the sense that the filler does notseparate from aqueous emulsion. Stainless steel, ordinary steel, lead,aluminum, glass, silicon, carbide, silica, aluminum oxide and titaniumoxide are examples of suitable filler materials.

At least about 1% by weight of filler based on PTFE is needed in theapplied PTFE emulsion to provide noticeably improved abrasionresistance. It is preferred to use at least about 5% of filler based onPTFE.

Curing Conditions The PTFE emulsion is applied to the dry textilesubstrate and after any excess emulsion has been drained off. Thestructure is air-dried and is then cured at a temperature from about 340C. to about 400 C. Generally a temperature of about 390 C. for from 5 to40 minutes is preferred. Higher temperatures can be employed to re duceexposure periods at curing temperatures.

Final Structure and After-Treatment The final structure has thesuppleness and flexibility characteristic of a textile. Generally acoating of from about to 60% of the total Weight of the final structureprovides the desired properties. When as much as 80% coating is applied,suppleness of the structure is reduced. Generally, it is preferred toemploy about 50% of coating based on the weight of the final structure.Once the PTFE coating has been cured, no further after-treatments arenecessary; however, it may be desirable to calender, emboss or laminatethe final product. The structure of the present invention is adaptableto such operations as readily as is one which contains no filler.

4 UTILITY The textiles of the present invention are useful as hightemperature shields, antistatic linings, car tops and headliners,non-sticking surfaces, non-flammable paddings, packing seals,high-temperature and abrasive resistance belts, shields against radiofrequency and microwave energy, filter cloths, anti-friction bearingsand carpeting.

Many equivalent modifications will become apparent to those skilled inthe art from a reading of the above without a departure from theinvention concept.

What is claimed is:

1. A structure comprising a fabric made up of a high melting textilesubstrate bearing an antistatic coating of polytetrafluoroethylene in anamount of from about 10- based on Weight of the fabric, said coatingcontaining from about 0.5 to about 30% by weight, based on the coating,of a filler of hard, water insoluble particulate matter having aparticle size of at least one micron in diameter and selected from thegroup of metals consisting of aluminum and stainless steel.

2. The structure of claim 1 wherein the textile substrate is glass.

3. The structure of claim 2 wherein the textile substrate is fiberglass.

4. The structure of claim 3 wherein the filler is aluminum.

5. The structure of claim 3 wherein the filler is stainless steel.

6. The structure of claim 5 wherein particle size distribution of thestainless steel filler is such that 100% is less than 74 microns, 98% isless than 44 microns, is less than 20 microns and 31% is less than 10microns.

7. A process of'making the structure of claim 1 which comprises sprayingan emulsion containing about 50% by weight of polytetrafluoroethyleneand from about .2% to about 15% by weight of a filler of hard, waterinsoluble particulate matter of at least micron size and selected fromthe group of metals consisting of aluminum and stainless steel upon ahigh melting textile substrate to form a coating on said substrate andthereafter curing the coating by subjecting it to a temperature of from340 C. to 400 C. for a period of from about 5 minutes to 40 minutes.

References Cited UNITED STATES PATENTS 2,843,502 7/1958 Fay 117-653,202,626 8/1965 Fitzsimmons 260-29.6 F 3,573,230 3/1971 Voorhees 260-41B EDWARD G. WHITBY, Primary Examiner US. Cl. X.R.

28-74 R, R; 117-98, 124 E, 126 GM, 126 GR, 161 R; 161-83, 93, 158, 204,218; 260-29.6 F, 41 B

